Organic substitution is increasingly promoted as a sustainable strategy to enhance soil fertility and mitigate carbon (C) loss, yet how varying substitution ratios influence soil organic carbon (SOC) stabilization remains poorly understood. A decade-long field experiment was conducted on the Loess Plateau of China to investigate the influence of replacing synthetic fertilizers with manure on microbial life-history strategies and SOC persistence. Four fertilization treatments were compared: without fertilizer (CK), synthetic fertilizer (NP), 50 % organic substitution (NPM), and 100 % organic substitution (M). This study found that organic substitution significantly increased microbial necromass C (MNC) and lignin phenol accumulation. The NPM treatment increased MNC by 23.0 % compared to NP. Functional gene analysis revealed that NPM upregulated lignindegrading CAZymes (e.g., GH3, AA2) and exopolysaccharide biosynthesis genes in Proteobacteria-dominated communities, accelerating the conversion of plant-derived lignin into microbial necromass. In contrast, 100 % organic substitution (M) induced nitrogen limitation, shifting microbial strategies toward resource acquisition (A-strategy) via peptidoglycan decomposition (GH25, NAG). This decreased the stability of mineral-associated organic C (MAOC) compared to CK by promoting competitive substitution with labile C. Although total SOC was higher in the M-treated soil, the MAOC to SOC ratio was decreased by 21.3 % due to disturbed microbialmineral synergies. These findings demonstrate that 50 % manure substitution optimally balances C input and nutrient availability, promoting microbial growth efficiency and stabilizing SOC via microbial-mineral synergy. This study highlights the importance of microbial life-history strategies in regulating SOC dynamics and provides practical guidance for sustainable soil management in dryland agroecosystems.